1. Field of Invention
The present invention relates to an ink composition for ink-jet recording, an ink set, and an image forming method.
2. Description of the Related Art
In recent years, as a result of ever-increasing demand for the protection of resources, protection of the environment, enhancement of operational stability and the like, the conversion of coating materials and inks (hereinafter, also referred to as “inks”) into aqueous products is in progress. The product qualities demanded from aqueous coating materials and aqueous inks include fluidity, storage stability, glossiness of film, clarity, coloring ability and the like, as in the case of oily coating materials and oily inks. However, most pigments have a markedly poor adaptability to aqueous vehicles, such as pigment dispersibility, compared to the case of oily vehicles, and therefore, satisfactory product quality cannot be obtained by conventional dispersion methods. Heretofore, the use of various additives, for example, aqueous pigment dispersing resins or surfactants, has been examined, but an aqueous coating material or aqueous ink that satisfies all the adaptation properties described above and is comparable to the existing oily coating materials or oily inks having high product quality, has not been obtained.
In order to solve these problems, for example, there is disclosed an aqueous ink composition containing a colorant coated with a water-soluble polymer as a coloring material, and polymer particles (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-329199). An ink-jet ink utilizing this aqueous ink composition is believed to be excellent in water resistance, scratch resistance, marker resistance and printability.
There is also disclosed an ink composition containing at least a colorant coated with a water-insoluble polymer as a coloring material, and a resin emulsion as an additive, characterized in that the weight average molecular weight of the water-insoluble polymer is 50,000 to 150,000, and that the resin emulsion is formed from a polymer having components which are the same structure as those of the water-insoluble polymer and having a weight average molecular weight of 1.5-fold to 4-fold the molecular weight of the water-insoluble polymer (see, for example, JP-A No. 2006-273892). It is said that this ink has good glossiness and scratch resistance.
However, the images formed with the ink compositions described in JP-A No. 2001-329199 and JP-A No. 2006-273892 had improved scratch resistance, but could not be considered to have satisfactory blocking resistance.